Conventional tank heaters and, particularly, water heaters are subject to the accumulation of sediment at the bottom of the tank. In tank type water heaters, particles in the water settle out during heating and accumulate at the bottom to form a constantly expanding layer of scale. The scale promotes corrosion of the tank, inhibits heat conduction from the tank bottom to the water, and interferes with the fluid passageways. Eventually, the scale causes a premature breakdown of the tank heater.
To combat this problem, scale agitators have been developed. See, e.g., U.S. Pat. No. 4,263,879 to Lindahl and U.S. Pat. No. 4,257,355 to Cook. Typically, the scale agitators use a perforated tube within the tank. The incoming cold water supply to the heater tank is routed through the tube and sprayed out the perforations in different directions around the bottom of the tank to stir up the particles which have accumulated there. Forced into suspension in the water again, some of the particles are carried out the hot water outlet near the top of the tank when the hot water is used.
However, the scale agitator tubing is subject to the same scale particles as the tank. The perforations in the tube are easily clogged because they are so small. When the perforations are clogged, not only are particles allowed to accumulate on the bottom of the tank, but cold makeup water can no longer enter the tank. When this happens, the tube must be cleaned. Thorough cleaning requires that the tube be removed. Yet, in some designs, the tube is made of curved metal specifically adapted for the particular tank and cannot be removed. The entire tank must therefore be replaced. In addition, the metal tube places a cathodic load on the heater's anode protection system which increases the rate of anode consumption. Thus, in some instances, the presence of this type of scale agitator can actually shorten the lifetime of the heater.